There is a BIG dropoff in pay after the top 10-15 in the 1st Rd. Chris Johnson was drafted by the Titans at 24 in the 1st Rd. Adrian Peterson was in the top 5-10. Peterson was getting paid about $7mill/yr vs CJ making roughly 1-2mill/yr.
To make matters worse, they now have the rookie salary cap. They are going to be stuck with a relatively weak salary (compared to veterans) for their first 4-5yrs...if they make it that long.
That's why it's a worthwhile investment to sharpen your game as much as possible before heading into the league. 1yr can make them millions more over that 4-5yr contract. If they just rush in, Tyler Bray style (he went undrafted), they really stand to regret it.
I think Tiny, too could have benefited greatly from another year. NFL teams tend to view players from losing teams in a different light than those of winning/successful ones. Sometimes that stigma alone can mean the difference between a round or three.